Effect of thermal manipulation during embryogenesis on liver heat shock protein expression in chronic heat stressed colored broiler chickens

Early life thermal conditioning alters heat-shock protein expression in response to an adult thermal stressor

Developmental environmental stressors can have instructive effects on an organism's phenotype. This developmental plasticity can prepare organisms for potentially stressful future environments, circumventing detrimental effects on fitness. However, the physiological mechanisms underlying such adaptive plasticity are understudied, especially in vertebrates. We hypothesized that captive male zebra finches (Taeniopygia castanotis) exposed to a mild heat conditioning during development would acquire a persisting thermotolerance, and exhibit increased heat-shock protein (HSP) levels associated with a decrease in oxidative damage when exposed to a high-intensity stressor in adulthood. To test this, we exposed male finches to a prolonged mild heat conditioning (38°C) or control (22°C) treatment as juveniles. Then in a 2 × 2 factorial manner, these finches were exposed to a high heat stressor (42°C) or control (22°C) treatment as adults. Following the adult treatment, we collected testes and liver tissue and measured HSP70, HSP90, and HSP60 protein levels. In the testes, finches exhibited lower levels of HSP90 and HSP60 when exposed to the high heat stressor in adulthood if they were exposed to the mild heat conditioning as juveniles. In the liver, finches exposed to the high heat stressor in adulthood had reduced HSP90 and HSP60 levels, regardless of whether they were conditioned as juveniles. In some cases, elevated testes HSP60 levels were associated with increased liver oxidative damage and diminishment of a condition-dependent trait, indicating potential stress-induced tradeoffs. Our results indicate that a mild conditioning during development can have persisting effects on HSP expression and acquired thermotolerance.

Comparison of selenium-mediated regulation of heat shock protein and inflammation in-vitro and in-ovo for heat resistance enhancement in broiler

Selenium is a heat-stress-reducing substance that improves heat resistance and is being studied for its effective application in the broiler industry. However, research on feed additives is labor-intensive and time-consuming because of the need for feeding experiments. We aimed to compare the effects of selenium under heat stress in vitro and in ovo, specifically examining the gene expression of heat shock proteins (HSP) and inflammatory markers. Two groups were included in the in-vitro study: in-vitro control (TC; selenium 0 μg/ml) and in-vitro selenium (TS; selenium 5 μg/ml). The satellite cells were cultured at 42°C for 48 h after selenium treatment. The in-ovo study comprised 4 groups: in-ovo control and in-ovo selenium 1-3 (OC, OS1, OS2, and OS3; selenium 2.5, 5, and 10 μg/egg, respectively). Selenium was injected on the 18th day after hatching, and heat treatment was performed at 32-34°C from the 14th to the 21st day after hatching, and the leg muscles of the chicks were collected on the 21st day. The gene expression of heat shock proteins (HSP), caspase3, nuclear factor kappa light-chain enhancer of activated B cells (NF-kB), and IL-8 was analyzed in in-vitro and in-ovo experiments, respectively. In-vitro results showed significant increases in HSP90, HSP60, and HSP40 in TS compared to TC, with a significant decrease in HSP70. In the in-ovo study, HSP70, caspase3, NF-kB and IL-8 were significantly increased in OS1. HSP90, HSP60, HSP40, HSP27 and NF-kB were significantly decreased in in-ovo OS2 compared to in-vitro TS, implying a trend in ratio compared to control. Selenium appeared to enhance heat resistance in-vitro and in-ovo by modulating HSPs and inflammation. However, differences in mRNA expression were observed depending on the concentration of selenium. These findings suggest that selenium modulates heat resistance through different mechanisms in-vitro and in-ovo, likely due to the complexity of whole-organism interactions in-ovo compared to the single-cell-type environment in-vitro. Therefore, to directly apply in-vitro results to in-ovo, a concentration comparison study for each additive is necessary.

Growth performance, blood biochemistry, and mRNA expression of hepatic heat shock proteins of heat-stressed broilers in response to rosemary and oregano extracts

The growing interest in countering the adverse effects of heat stress in poultry using phytogenic feed additives has garnered considerable attention in recent times, this research sought to examine the impact of rosemary leaves extract (RLE) and oregano leaves extract (OLE) on the growth performance, physiological responses, and hepatic mRNA expression of heat shock proteins in broiler chickens exposed to heat stress. A total of 150 male Indian River chicks, aged one day, were randomly allocated into five equally sized groups, each consisting of six replicates. The initial group was designated as the control and was provided with the basal diet. The second and third groups (R1 and R2) were administered the basal diet enriched with 50 and 100 mg/kg of rosemary leaves extract (RLE), respectively. The fourth and fifth groups (O1 and O2) were fed the basal diet supplemented with 50 and 100 mg/kg of oregano leaves extract (OLE), respectively. These chicks were reared in a controlled environmental chamber maintained at a temperature of 32±2 °C and relative humidity of 50 ± 5 %. Ferruginol was the leading component in RLE, whereas thymol was the prevalent constituent in OLE. RLE and OLE both have high DPPH• and ABTS•+ antioxidant potential. Among the experimental groups, the fourth group (O1) showed the heaviest live body weight and the lowest feed conversion ratio, indicating improved growth performance. There was a significant reduction in plasma total lipids and LDL-cholesterol levels within the R2 and O2 groups, respectively. Enhanced total antioxidant capacity and an improvement in the T3 hormone were observed in the R1 and R2 groups. In the second and fourth groups, the mRNA expression of hsp70 and 90A were both found to be significantly downregulated, respectively. In conclusion, the addition of 50 mg/kg of oregano leaves extract (OLE) to the diets of heat-stressed broilers resulted in improved hepatic heat shock proteins, along with certain physiological responses, ultimately contributing to enhanced growth performance.

Hepatic heat shock proteins, antioxidant-related genes, and immunocompetence of heat-stressed broilers in response to short periods of incubation during egg storage and thermal conditioning

Short Periods of Incubation During Egg Storage (SPIDES) approach improves chick quality and hatching rates. Also, embryonic thermal conditioning (TC) is a strategy for enhancing thermotolerance in avian species. Until now, evaluating the effect of either SPIDES or embryonic TC effects has only been separately conducted, so we hypothesized that combining TC and SPIDES may enhance the response of broilers to thermal stress. Eight hundred Ross broiler eggs were divided into two groups; the first one was kept under appropriate storage room conditions, S0 (control) The 2nd was subjected to SPIDES for 5 h at 37.8 ○C ± 0.1 three times at days 5, 10, and 15 (S1) after egg collection respectively. On the 14th day of incubation (DOI) each of the two main groups was randomly divided into two equal subgroups; the control one was left under the appropriate incubation settings (TC0) whereas the other received prenatal heat conditioning (TC1) at 39.5 ○C ± 0.1 for 6 h/d from the 14th to the 18th embryonic day (E), resulting finally in four experimental subgroups (S0TC0, S1TC0, S0TC1 & S1TC1). RESULTS: showed that SPIDES treatment improved the hatchability of the stored eggs by almost 20% compared to untreated eggs. A combination of SPIDES and TC (S1TC1) increased significantly the levels of Immunoglobulin (IgG and IgM) production at hatch and heat-stressed birds. Our findings revealed that the hepatic heat shock proteins (hsp70, 90 A,90 B, 60 and hspA9), antioxidants-related genes (CAT, and SOD2), and NADPH4 were significantly downregulated in the thermally conditioned group that challenged with thermal stress conditions. As opposed to that, the SPIDES group showed a significant increase in hepatic heat shock proteins, antioxidants-related genes, and NADPH4 when subjected to thermal-stress conditions. In conclusion, the combination of SPIDES and TC has a positive effect on some pre and post-hatch traits of broiler chicks. Under heat stress challenge, thermal conditioning can modify the expression of antioxidant-related genes and Hsps, leading to the enhanced acquisition of thermotolerance as evidenced by lower expression of Hsps and NADPH4. While SPIDES does not have a significant role in thermotolerance acquisition.

Heat Shock Protein Response to Stress in Poultry: A Review

Compared to other animal species, production has dramatically increased in the poultry sector. However, in intensive production systems, poultry are subjected to stress conditions that may compromise their well-being. Much like other living organisms, poultry respond to various stressors by synthesising a group of evolutionarily conserved polypeptides named heat shock proteins (HSPs) to maintain homeostasis. These proteins, as chaperones, play a pivotal role in protecting animals against stress by re-establishing normal protein conformation and, thus, cellular homeostasis. In the last few decades, many advances have been made in ascertaining the HSP response to thermal and non-thermal stressors in poultry. The present review focuses on what is currently known about the HSP response to thermal and non-thermal stressors in poultry and discusses the factors that modulate its induction and regulatory mechanisms. The development of practical strategies to alleviate the detrimental effects of environmental stresses on poultry will benefit from detailed studies that describe the mechanisms of stress resilience and enhance our understanding of the nature of heat shock signalling proteins and gene expression.

Acute exposure to high temperature affects expression of heat shock proteins in altricial avian embryos

As the world warms, understanding the fundamental mechanisms available to organisms to protect themselves from thermal stress is becoming ever more important. Heat shock proteins are highly conserved molecular chaperones which serve to maintain cellular processes during stress, including thermal extremes. Developing animals may be particularly vulnerable to elevated temperatures, but the relevance of heat shock proteins for developing altricial birds exposed to a thermal stressor has never been investigated. Here, we sought to test whether three stress-induced genes - HSPD1, HSPA2, HSP90AA1 - and two constitutively expressed genes - HSPA8, HSP90B1 - are upregulated in response to acute thermal shock in zebra finch (Taeniopygia guttata) embryos half-way through incubation. Tested on a gradient from 37.5 °C (control) to 45 °C, we found that all genes, except HSPD1, were upregulated. However, not all genes initiated upregulation at the same temperature. For all genes, the best fitting model included a correlate of developmental stage that, although it was never significant after multiple-test correction, hints that heat shock protein upregulation might increase through embryonic development. Together, these results show that altricial avian embryos are capable of upregulating a known protective mechanism against thermal stress, and suggest that these highly conserved cellular mechanisms may be a vital component of early developmental protection under climate change.

Effects of Thermal Manipulation on mRNA Regulation of Response Genes Regarding Improvement of Thermotolerance Adaptation in Chickens during Embryogenesis

The phenomenon of increasing heat stress (HS) among animals is of particular significance when it is seen in economically significant industries, such as poultry. Due to the identification of the physiological, molecular, and genetic roots of HS responses in chickens, a substantial number of studies have focused on reducing the effects of HS in poultry through environmental management, dietary manipulation, and genetic alterations. Temperature manipulation (TM) during embryogenesis has been claimed to increase the thermal tolerance and well-being of chickens without affecting their capacity for future growth. There has been little investigation into the vulnerability of the epigenome involving TM during embryogenesis, although the cellular pathways activated by HS have been explored in chickens. Epigenetic changes caused by prenatal TM enhance postnatal temperature adaption and produce physiological memory. This work offers a thorough analysis that explains the cumulative impact of HS response genes, such as genes related to heat shock proteins, antioxidants, and immunological genes, which may aid in the enhanced adaptability of chickens that have undergone thermal manipulation during their embryonic stages.

L-serine improves lipid profile, performance, carcass weight and intestinal parameters in feed restricted broiler chickens during the hot-dry season

The study evaluated effects of L-serine on lipid profile, performance, carcass weight and small intestinal parameters in heat-stressed broiler chickens subjected to feed restriction. Broiler chickens were divided into four groups, comprising 30 each. Group 1, feed restriction (FR); Group 2, feed restriction + L-serine (200 mg/kg) (FR + L-serine); Group 3, ad libitum (AL); Group 4, ad libitum + L-serine (200 mg/kg) (AL + L-serine). L-serine was administered orally from days 1 to 14, and feed restriction was performed on days 7-14. Serum harvested from blood samples on days 21, 28 and 35 was evaluated for lipid profile. Feed and water intake, live weight gain, organ and carcass weight were measured. At 35 days old, broiler chickens (n = 7) per group were sacrificed to evaluate small intestinal morphology. Temperature-humidity index in the pen (30.88 ± 0.81) was above thermoneutral zone, indicating that chickens were subjected to heat stress. Concentrations of low-density lipoprotein, total cholesterol and total triglycerides were lower (p < 0.05), while higher concentration of high-density lipoprotein was recorded in L-serine groups than in the controls. Feed intake and live weight gain on day 35 in L-serine groups were higher (p < 0.05) than in controls. In L-serine groups, liver, spleen, pancreas and heart weight were higher, but abdominal fat was lower than in FR and AL groups. Villus height:crypt height ratio and area of villus surface were highest in L-serine groups than any other group. In conclusion, L-serine decreased low-density lipoprotein, increased feed intake, live weight, organ and carcass weight, villus height:crypt height ratio and villus surface area.

Embryonic manipulations modulate differential expressions of heat shock protein, fatty acid metabolism, and antioxidant-related genes in the liver of heat-stressed broilers

In this study, the effects of in ovo feeding of γ-aminobutyric acid (GABA) and embryonic thermal manipulation (TM) on plasma biochemical parameters, organ weights, and hepatic gene expression in broilers exposed to cyclic heat stress (32 ± 1°C for 8 days) (HS) were investigated. A total of 175 chicks were assigned to five treatments: chicks hatched from control eggs (CON); chicks hatched from control eggs but exposed to HS (CON+HS); chicks hatched from eggs injected at 17.5 days of incubation with 0.6mL of 10% GABA and exposed to HS (G10+HS); chicks hatched from thermally manipulated eggs (39.6°C, 6h/d from embryonic days 10 to 18) and exposed to HS (TM+HS); chicks hatched from eggs that received both previous treatments during incubation and exposed to HS (G10+TM+HS). Results revealed that on day 36 post-hatch, hepatic NADPH oxidase 1 (P = 0.034) and 4 (P = 0.021) genes were downregulated in the TM+HS and G10+TM+HS compared to the CON+HS group. In addition, while acetyl-CoA carboxylase gene expression was reduced (P = 0.002) in the G10+TM group, gene expression of extracellular fatty acid-binding protein and peroxisome proliferator-activated receptor-γ was lower (P = 0.045) in the TM+HS group than in the CON+HS group. HS led to higher gene expression of heat shock protein 70 (HSP70) and 90 (HSP90) (P = 0.005, and P = 0.022). On the other hand, the TM+HS group exhibited lower expression of both HSP70 (P = 0.031) and HSP90 (P = 0.043) whereas the G10+TM+HS group had a reduced (P = 0.016) HSP90 expression compared to the CON+HS. MANOVA on different gene sets highlighted an overall lower (P = 0.034) oxidative stress and lower (P = 0.035) heat shock protein expression in the G10+TM+HS group compared to the CON+HS group. Taken together, the current results suggest that the combination of in ovo feeding of GABA with TM can modulate HSPs and antioxidant-related gene expression in heat-stressed broilers.

Mitigating the detrimental effects of heat stress in poultry through thermal conditioning and nutritional manipulation

The poultry industry faces several obstacles and challenges, including the changes in global temperature, increase in the per capita demand for meat and eggs, and the emergence and spread of various diseases. Among these, environmental challenges are one of the most severe hurdles impacting the growth and productivity of poultry. In particular, the increasing frequency and severity of heat waves over the past few years represent a major challenge, and this is expected to worsen in the coming decades. Chickens are highly susceptible to high ambient temperatures (thermal stress), which negatively affect their growth and productivity, leading to enormous economic losses. In the light of global warming, these losses are expected to increase in the near future. Specifically, the worsening of climate change and the rise in global temperatures have augmented the adverse effects of heat on poultry production worldwide. At present, the world population is approximately 7.9 billion, and it has been predicted to reach 9.3 billion by 2050 and approximately 11 billion by 2100, implying a great demand for protein supply; therefore, strategies to mitigate future poultry challenges must be urgently devised. To date, several mitigation measures have been adopted to minimize the negative effects of heat stress in poultry. Of these, thermal acclimation at the postnatal stage or throughout the embryonic stages has been explored as a promising approach; however, for large-scale application, this approach warrants further investigation to determine the suitable temperature and poultry age. Moreover, molecular mechanisms governing thermal conditioning are poorly understood. To this end, we sought to expand our knowledge of thermal conditioning in poultry, which may serve as a valuable reference to improve the thermotolerance of chickens via nutritional management and vitagene regulation. Vitagenes regulate the responses of poultry to diverse stresses. In recent years, nutritionists have paid close attention to bioactive compounds such as resveratrol, curcumin, and quercetin administered alone or in combination. These compounds activate vitagenes and other regulators of the antioxidant defense system, such as nuclear factor-erythroid 2-related factor 2. Overall, thermal conditioning may be an effective strategy to mitigate the negative effects of heat stress. In this context, the present review synthesizes information on the adverse impacts of thermal stress, elucidating the molecular mechanisms underlying thermal conditioning and its effects on the acquisition of tolerance to acute heat stress in later life. Finally, the role of some polyphenolic compounds, such as resveratrol, curcumin, and quercetin, in attenuating heat stress through the activation of the antioxidant defense system in poultry are discussed.

Environmental Stress in Chickens and the Potential Effectiveness of Dietary Vitamin Supplementation

Environmental stressors can promote the vulnerability of animals to infections; it is therefore, essential to understand how stressors affect the immune system, the adaptive capacity of animals to respond, and effective techniques in managing stress. This review highlights scientific evidence regarding environmental stress challenge models and the potential effectiveness of vitamin supplementation. The major environmental stressors discussed are heat and cold stress, feed restriction, stocking density, and pollutants. Much work has been done to identify the effects of environmental stress in broilers and layers, while few involved other types of poultry. Studies indicated that chickens' performance, health, and welfare are compromised when challenged with environmental stress. These stressors result in physiological alterations, behavioral changes, decreased egg and meat quality, tissue and intestinal damage, and high mortalities. The application of vitamins with other nutritional approaches can help in combating these environmental stressors in chickens. Poultry birds do not synthesize sufficient vitamins during stressful periods. It is therefore suggested that chicken diets are supplemented with vitamins when subjected to environmental stress. Combination of vitamins are considered more efficient than the use of individual vitamins in alleviating environmental stress in chickens.

Thyroid hormones and Corticosterone investigation under heat stress in native chicken

The study was conducted to evaluate the effect of thermal conditioning on serum levels of Triiodothyronine (T3), thyroxine (T4) and corticosterone (CORT) in four different chicken strains namely Aseel, Naked Neck, Assel × Nandanam chicken-4 and Naked Neck × Nandanam Broiler-3. Chicks were divided into control (C; ambient temperature 28±1°C) and heat exposed groups (H; 39±1°C for 2 hours; 0-2 and 5-6 weeks of age). At 12th week, control group were divided into two groups, i.e. unexposed control (C) and exposed control (CE). Birds from H group (HE) and CE group were thermally challenged at 39±1°C for 4 hours daily on 12th week. On 42nd and 84th day, blood was withdrawn from each group, serum separated and processed for T3, T4 and CORT. The results indicated that the thermal conditioning had significantly decreased T3, T4 and increased CORT levels, irrespective of strains. At thermal challenge, a drastic drop in CORT level and improvement in thyroid hormone levels were noticed in the preconditioned birds. From present study, it was concluded that, the birds are able to withstand the heat stress effect which was indicated by drop in CORT level.

Early heat exposure effect on the heat shock proteins in broilers under acute heat stress

The effects of early heat conditioning on the acute heat stress response in broilers were investigated via the growth performance, dopamine, serotonin, and corticosterone and the expression of heat shock proteins (HSP) and heat shock factors. One-day-old chicks (n = 144) were divided into 3 groups in a 35-d experiment (48 chicks per each group). Group 1 (C) was treated with an optimum temperature, group 2 (CH) was treated with 40°C ± 1°C on day 35 (5 h), and group 3 (HH) was treated with 40°C ± 1°C on day 5 (24 h) and day 35 (5 h). On day 7, the body weight gain was lower (P < 0.05) in HH than in C and CH. On day 35, the heat-treated groups (CH and HH) had lower weight gains than the C group (P < 0.05), whereas the feed conversion ratio was lower in HH (P < 0.05). Serum corticosterone was higher in CH than in C, but HH and C did not differ (P < 0.05). Liver HSP70 protein expression was higher in CH than HH and C (P < 0.05), which did not differ, and HSP40 protein expression was higher in CH than C (P < 0.05). These results suggest that early heat conditioning may reduce acute heat stress on broiler.

Climate change and heat stress: Impact on production, reproduction and growth performance of poultry and its mitigation using genetic strategies

Heat stress is an important environmental determinant which adversely affects the performance of poultry worldwide. The present communication reviews the impact of heat stress on production, reproduction and growth performance of poultry, and its alleviation using genetic strategies. The adverse effects of high environmental temperature on poultry include decrease in growth rate, body weight, egg production, egg weight, egg quality, meat quality, semen quality, fertility and hatchability, which cause vast financial losses to the poultry industry. High ambient temperature has an antagonistic effect on performance traits of the poultry. Thus, selection of birds for high performance has increased their susceptibility to heat stress. Additionally, heat burden during transportation of birds from one place to another leads to reduced meat quality, increased mortality and welfare issues. Molecular markers are being explored nowadays to recognize the potential candidate genes related to production, reproduction and growth traits for selecting poultry birds to enhance thermo-tolerance and resistance against diseases. In conclusion, there is a critical need of formulating selection strategies based on genetic markers and exploring more genes in addition to HSP25, 70, 90, H1, RB1CC, BAG3, PDK, ID1, Na, F, dw and K responsible for thermoregulation, to improve the overall performance of poultry along with their ability to tolerate heat stress conditions.

Differential expression of small heat shock proteins in the brain of broiler embryo; the effects of embryonic thermal manipulation

Broilers are more vulnerable to high temperatures than mammals due to the feather cover, lack of sweat glands, fast growth and intensive breeding in commercial systems. Thermal stresses affect the function of various organs and change the expression profiles of hundreds of genes in the different tissues of broilers. Thermal manipulation (TM) during embryogenesis can increase heat tolerance in growing broilers. Small heat shock proteins (SHSPs) are a group of HSPs which participate in many cellular functions like response to different stressors. However, their role in the thermotolerance has not been fully elucidated. Ninety fertilized eggs were randomly divided into three groups (30 eggs/group; 10 eggs/replicate). Normal control (NC) eggs were incubated at 37.5 °C throughout the incubation period whereas heat stress (HS) and cold stress (CS) groups were kept at 41 °C and 33 °C from 15 to 17th day of incubation for 3 h each day, respectively. On day 20, samples from the cerebrums were harvested for histopathology and mRNA expression analyses of HSPB1, HSPB5, HSPB8, and HSPB9. There were no significant differences in survivability, defected embryos, hatchability, and body weight among treatments. TM had no major deleterious effects on the cerebral tissue except for mild degeneration in the HS group. HSPB1, HSPB5, HSPB8, and HSPB9 were expressed in the presence and absence of TM. All SHSP genes tested were downregulated in response to TM except for HSPB9 which was upregulated in the HS group. The highest change in gene expression due to TM observed for HSPB1. This study presents a broader understanding of mechanisms underlying response to TM in broilers. The results suggest that HSPB1, HSPB5, HSPB8, and HSPB9 are involved in thermotolerance in broilers and SHSPs could be involved in the gene expression profiling of TM. It may propose the use of nutritional supplements in the poultry industry to modulate SHSPs.

Effects of thermal manipulation of eggs on the response of jejunal mucosae to posthatch chronic heat stress in broiler chickens

In this study, the aim was to investigate effects of chronic heat stress (CHS) on the mRNA levels of proinflammatory cytokines (interleukin [IL]-6, IL-8, IL-1β, and tumor necrosis factor alpha [TNF-α]), toll-like receptors (TLR2 and TLR4), heat shock proteins (Hsp70, heat shock transcription factor [HSF]-1, and HSF3) and antioxidant enzymes (catalase, glutathione peroxidase, NADPH oxidase, and superoxide-dismutase) in the jejunal mucosae of broiler chickens subjected to thermal manipulation (TM) during embryogenesis. TM was carried out at 39°C and 65% relative humidity (RH) for 18 h daily from embryonic days 10 to 18. Control group was incubated at 37.8°C and 56% RH. CHS was induced by raising the temperature to 35°C for 7 D throughout posthatch days 28 to 35. On post-hatch-day 28 (day zero of CHS) and after 1, 3, 5, and 7 D of CHS, the jejunal mucosae were collected from both groups to evaluate the mRNA levels by real-time reverse transcription-PCR analysis. On day zero of CHS, the mRNA levels of antioxidant enzymes, TLRs, HSF3, IL-1β, and TNF-α were not significantly different between TM and control groups, while the levels of IL-6, IL-8, and HSF1 were lower and the level of Hsp70 was higher in TM. However, during CHS, the mRNA levels of antioxidant enzymes, IL-1β, TNF-α, TLR4, and HSF1 were significantly lower in TM than in controls, while the levels of TLR2 and IL-8 were significantly higher in TM than in controls. In addition, TM led to significant increase of mRNA levels of IL-6 and HSF3 after 1 D and Hsp70 after 3 D of CHS and to significant decrease of mRNA levels of IL-6 after 3 and 5 D, HSF3 after 7 D, and Hsp70 after 5 D of CHS. Results of this study suggest that TM led to altered posthatch antioxidant, immunological, and Hsp response to CHS in the jejunal mucosae of broiler chickens, probably indicating that TM may mitigate the adverse effects of CHS.

Identification of Metabonomics Changes in Longissimus Dorsi Muscle of Finishing Pigs Following Heat Stress through LC-MS/MS-Based Metabonomics Method

Simple Summary

Limited research exists on muscle metabolomics of finishing pigs under heat stress. In this study, nine different metabolites in the longissimus dorsi (LD) muscle of finishing pigs under heat stress were screened and identified. Through quantitative verification, it was concluded that the content of L-carnitine in the LD muscles of the finishing pigs could be significantly decreased due to heat stress, which might be a biomarker for monitoring the animal health status and muscle quality under heat stress.

Abstract

Heat stress (HS) negatively affects meat quality by affecting material and energy metabolism, and exploring the mechanism underlying the muscle response to chronic HS in finishing pigs is important for the global pork industry. This study investigated changes in the metabolic profiles of the longissimus dorsi (LD) muscle of finishing pigs under high temperature using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOF-MS) and multivariate data analysis (MDA). Castrated male DLY pigs (Duroc × Landrance × Yorkshire pigs, n = 24) from 8 litters were divided into three treatment groups: constant optimal ambient temperature at 22 °C and ad libitum feeding (CR, n = 8); constant high ambient temperature at 30 °C and ad libitum feeding (HS, n = 8); and constant optimal ambient temperature 22 °C and pair-feeding to the control pigs (PF, n = 8). The metabolic profile data from LD muscle samples were analyzed by MDA and external search engines. Nine differential metabolites (L-carnosine, acetylcholine, inosinic acid, L-carnitine, L-anserine, L-α-glycerylphosphorylcholine, acetylcarnitine, thiamine triphosphate, and adenosine thiamine diphosphate) were involved in antioxidant function, lipid metabolism, and cell signal transduction, which may decrease post mortem meat quality and play important roles in anti-HS. Four metabolites (L-carnosine, acetylcholine, inosinic acid, and L-carnitine) were verified, and it was indicated that the muscle L-carnitine content was significantly lower in HS than in CR (p < 0.01). The results show that constant HS affects the metabolites in the LD muscle and leads to coordinated changes in the endogenous antioxidant defense and meat quality of finishing pigs. These metabonomics results provide a basis for researching nutritional strategies to reduce the negative effects of heat stress on livestock and present new insights for further research.

Expression of digestive enzyme and intestinal transporter genes during chronic heat stress in the thermally manipulated broiler chicken

Heat stress has a serious impact on nutrient digestion and absorption in broiler chickens. This study aimed to investigate the effects of chronic heat stress (CHS) on the mRNA expression of digestive enzymes and nutrient transporter genes in thermally manipulated (TM) broiler chickens. The evaluated genes encompassed pancreatic lipase, trypsin, amylase, maltase, and alkaline phosphatase as well as certain glucose transporter (GLUT2, SGLT1), amino acid transporter (y+LAT1, CAT1), and fatty acid transporter (FABP1, CD36) genes in the jejunal mucosa. Thermal manipulation was carried out at 39°C and 65% relative humidity for 18 h daily from embryonic days (ED) 10-18, while CHS was induced by raising the temperature to 35°C for 7 D throughout post-hatch days 28 to 35. After 0, 1, 3, 5, and 7 D of CHS, the pancreas and jejunal mucosa were collected from the control and TM groups to evaluate the mRNA expression by relative-quantitative real-time qRT-qPCR. Thermal manipulation significantly decreased the cloacal temperature (Tc) and the hatchling weight, and improved weight gain in broilers during post-hatch life and CHS. In addition, TM decreased the mortality rate during CHS. During CHS, the mRNA expression levels of SGLT1, GLUT2, FABP1, and trypsin were significantly decreased after 1 D in control chickens, and this lower expression persisted until day 7, after which it further decreased. In contrast, in TM chickens, SGLT1, GLUT2, and FABP1 expression decreased after 3, 5, and 7 D of CHS, respectively, while no significant change in trypsin expression was observed throughout the CHS period. Moreover, it was found that TM significantly modulated the mRNA expression dynamics of CD36, alkaline phosphatase, y+LAT1, CAT1, lipase, amylase, and maltase during CHS exposure. The findings of this study suggest that, in broiler chickens, TM has a long-lasting impact on nutrient digestion and absorption capabilities as well as Tc, mortality rates, and BW during CHS.

Heat Treatment at an Early Age Has Effects on the Resistance to Chronic Heat Stress on Broilers

This study was conducted to investigate the effects of early heat conditioning on growth performance, liver-specific enzymes (GOT and GPT), neuro-hormones (dopamine and serotonin), stress hormones (corticosterone), and the expression of HSPs (heat shock proteins), HSFs (heat shock factors), and pro-inflammatory cytokines under chronic high temperature. Broilers were raised with commercial feed and supplied with water ad libitum under conventional temperature. We separated the broilers into three groups: the control without any heat exposure (C), chronic heat-stressed group (CH), and early and chronic heat-stressed group (HH). At 5 days of age, the HH group was exposed to high temperatures (40 °C for 24 h), while the remaining groups were raised at a standard temperature. Between days 6 and 20, all three groups were kept under optimal temperature. From 21 to 35 days, the two heat-stressed groups (CH and HH) were exposed to 35 °C. Groups exposed to high temperature (CH and HH) showed significantly lower body weight and feed intake compared to the control. GOT and GPT were lower expressed in the CH and HH groups than the control group. In addition, the protein expressions of HSPs were down-regulated by chronic heat stress (CH and HH groups). The gene expressions of HSP60 and HSF3 were significantly down-regulated in the CH and HH groups, while HSP70 and HSP27 genes were up-regulated only in the HH group compared with the control group. The expression of pro-inflammatory cytokine genes was significantly up-regulated in the HH group compared with the control and CH groups. Thus, exposure of early Heat stress (HS) to broilers may affect the inflammatory response; however, early heat exposure did not have a positive effect on chronic HS of liver enzymes and heat shock protein expression.

Impact of exposure time to harsh environments on physiology, mortality, and thermal comfort of day-old chickens in a simulated condition of transport

The aim of this study was to assess the variation of physiological responses and mortality of day-old chicks subjected to different thermal conditions and exposure times during simulated transport. For this purpose, day-old chicks (n = 900) were used and subjected to simulated conditions of transport in a climate chamber. The experimental design was a completely randomized block design, with the structure of the treatments in a 3 × 3 factorial scheme (thermal ranges and time intervals) and each level of containers considered a block. The physiological variables used in this trial were body weight, respiratory rate, cloacal temperature, average surface temperature, and gene expression of heat shock protein (HSP70). Regarding body weight, a small variation was observed between treatments (P > 0.05). The animals subjected to the heat treatment exhibited respiratory rates above 100 movements per minute (P < 0.05), average cloacal temperatures above 44.7 °C, surface temperatures above the comfort zone (greater than 39.6 °C; P < 0.05), and increased gene expression of HSP70 (P < 0.001), especially after 3 initial hours of exposure. In addition, the heat treatment lead to increased mortality of the animals (over 6%). Also in the cold treatment, despite the absence of mortality, the animals showed hypothermia from 3 h of exposure, based on the results of the average surface (28 °C) and cloacal temperatures (39.6 °C; P < 0.05). In this way, the results imply that the effects of thermal stress caused by heat as well as by cold in a simulated transport condition are increased when traveling for more than 3 h, indicating a trend of rising mortality after long-term transportation of day-old chickens.

Effects of pre-hatch thermal manipulation and post-hatch acute heat stress on the mRNA expression of interleukin-6 and genes involved in its induction pathways in 2 broiler chicken breeds

In response to heat stress, interleukin-6 (IL-6) expression is upregulated in broiler chickens. The main aim of the present study was to evaluate the cumulative effects of thermal manipulation (TM) and subsequent acute heat stress (AHS) on the mRNA expression of IL-6 and genes involved in its induction pathways. The studied genes include IL-6, IL-1β, TNF-α, TLR2, TLR4, NFκB50, NFκB65, Hsp70, and HSF3 in the spleen and liver tissues. TM was carried out at 39°C for 18 h and 65% relative humidity during days 10 to 18 of embryonic development, while AHS was stimulated by raising the temperature to 40°C for 7 h on post-hatch day 28. During AHS at 0, 1, 3, 5, and 7 h, the spleen and liver were collected from all groups to measure the mRNA expression by relative-quantitation real-time RT-PCR, and the blood was collected to measure plasma IL-6 level. TM significantly reduced Tc during AHS for both breeds from 1 to 7 h time intervals. TM resulted in enhanced basal mRNA expression of IL-6, HSF3, and Hsp70, but decreased the basal mRNA level of TLR4. During heat stress, TM enhanced the expression dynamics of Hsp70, HSF3, IL-6, IL-1β, TNF-α, TLR2, TLR4, NFκB50, and NFκB65. The results of the current study indicate that TM enhanced the heat tolerance through improving the protective immunological response to heat stress by enhancing the expression of IL-6 and modulating the expression of genes important in its induction pathways.

Effect of thermal manipulation of broilers embryos on the response to heat-induced oxidative stress

Effects of embryonic thermal manipulation (TM) on mRNA expressional levels and total antioxidant capacity of genes associated with heat-induced oxidative stress (NOX4, GpX2, SOD2, catalase, and AvUCP) in 2 breeds of broiler chicken were investigated. Fertile Cobb and Hubbard eggs (n = 1,200) were divided into 4 treatment groups: Cobb control, Cobb TM, Hubbard control, and Hubbard TM. Control groups were maintained under standard conditions (37.8°C; 56% relative humidity), whereas TM groups were incubated at 39°C and 65% relative humidity for 18 h a day from embryonic days (ED) 10 to 18. On post-hatch day 28, the broilers were subject to acute heat stress (AHS) at 40°C for 7 h. At certain intervals (0, 1, 3, 5, and 7 h), 12 chickens from each of the 4 groups were humanely euthanized, and liver samples were immediately isolated. During AHS, in both breeds, the mRNA expression levels of NOX4, GPx2, SOD2, and catalase in TM chickens were significantly lower than in controls, but AvUCP mRNA expression in the TM group was higher. The total antioxidant capacity and activity of superoxidase dismutase and catalase were significantly lower in the TM than in the control group in both breeds. The results of this study suggest that TM has a long-lasting effect on the acquisition of thermotolerance in 2 broiler chicken breeds as indicated by the reduction of system genes associated with heat-induced oxidative stress.

Chronic Heat Stress Damages Small Intestinal Epithelium Cells Associated with the Adenosine 5'-Monophosphate-Activated Protein Kinase Pathway in Broilers

Heat-stressed broilers usually reduce their feed intake, leading to energy imbalance and disturbing the homeostasis in the small intestine. This study was aimed to explore heat-stress-mediated physiological features that may be ascribed to impairments in the intestinal tract of broilers. The results revealed that heat exposure increased the activities of trypsin and Na⁺/K⁺-ATPase, while it decreased the activities of amylase, lipase, and maltase as well as the proliferating cell nuclear antigen cells in the jejunum after 14 days of heat exposure. Meanwhile, heat stress upregulated the mRNA expressions of AMPKα1, LKB1, and HIF-1α and protein expressions of p-AMPKα^Thr172 and p-LKB1^Thr189 in the small intestine after 7 or 14 days of heat exposure. In conclusion, chronic heat exposure impeded the development of digestive organs, disordered the activities of intestinal digestive enzymes, and impaired the intestinal epithelial cells by increasing the cell apoptosis and declining cell proliferation, which might be correlated with the adenosine 5'-monophosphate-activated protein kinase signaling pathway. Additionally, heat stress upregulated the gene expression of HIF-1α, which indicated that heat stress may disturb the homeostasis in the intestine.

Evaluation of DNA methylation and mRNA expression of heat shock proteins in thermal manipulated chicken

Thermal manipulation during embryogenesis has been demonstrated to enhance the thermotolerance capacity of broilers through epigenetic modifications. Heat shock proteins (HSPs) are induced in response to stress for guarding cells against damage. The present study investigates the effect of thermal conditioning during embryogenesis and thermal challenge at 42 days of age on HSP gene and protein expression, DNA methylation and in vitro luciferase assay in brain tissue of Naked Neck (NN) and Punjab Broiler-2 (PB-2) chicken. On the 15th day of incubation, fertile eggs from two breeds, NN and PB-2, were randomly divided in to two groups: control (C)-eggs were incubated under standard incubation conditions, and thermal conditioning (TC)-eggs were exposed to higher incubation temperature (40.5°C) for 3 h on the 15th, 16th, and 17th days of incubation. The chicks obtained from each group were further subdivided and reared under different environmental conditions from the 15th to the 42nd day as normal [N; 25 ± 1 °C, 70% relative humidity (RH)] and heat exposed (HE; 35 ± 1 °C, 50% RH) resulting in four treatment groups (CN, CHE, TCN, and TCHE). The results revealed that HSP promoter activity was stronger in CHE, which had lesser methylation and higher gene expression. The activity of promoter region was lesser in TCHE birds that were thermally manipulated at the embryonic stage, thus reflecting their stress-free condition. This was confirmed by the lower level of mRNA expression of all the HSP genes. In conclusion, thermal conditioning during embryogenesis has a positive impact and improves chicken thermotolerance capacity in postnatal life.

l-Leucine acts as a potential agent in reducing body temperature at hatching and affords thermotolerance in broiler chicks

Thermal manipulation (TM) of incubation temperature causes metabolic alterations and contributes to improving thermotolerance in chicks post hatching. However, there has been no report on amino acid metabolism during TM and the part it plays in thermotolerance. In this study, we therefore first analyzed free amino acid concentrations in the embryonic brain and liver during TM (38.6°C, 6h/d during embryonic day (ED) 10 to ED 18). It was found that leucine (Leu), phenylalanine and lysine were significantly decreased in the embryonic brain and liver. We then chose l-Leu and other branched-chain amino acids (l-isoleucine (L-Ile) and l-valine (l-Val)) for in ovo injection on ED 7 to reveal their roles in thermoregulation, growth, food intake and thermotolerance in chicks. It was found that in ovo injection of l-Leu, but not of l-Ileu or l-Val, caused a significant decline in body temperature at hatching and increased food intake and body weight gain in broiler chicks. Interestingly, in ovo injection of l-Leu resulted in the acquisition of thermotolerance under high ambient temperature (35±1°C for 180min) in comparison with the control thermoneutral temperature (28±1°C for 180min). These results indicate that the free amino acid concentrations during embryogenesis were altered by TM. l-Leu administration in eggs caused a reduction in body temperature at hatching, and afforded thermotolerance in heat-exposed young chicks, further suggesting that l-Leu may be one of the key metabolic factors involved in controlling body temperature in embryos, as well as in producing thermotolerance after hatching.